Hydraulic cam motor

ABSTRACT

A compressed fluid driven downhole cam motor ( 1 ) of the type used during drilling/service operations in the ground, comprising an intermediate casing ( 4 ), a distributing valve ( 26 ), a rotor ( 18 ) and two or more pistons ( 48 ) arranged radially and distributed with equal or unequal separation about the central axis of the rotor ( 18 ), whereby the pistons ( 48 ) located in the same radial plane constitute a set of pistons, and where two or more sets of pistons are arranged side by side along the longitudinal axis of the rotor ( 18 ).

This invention regards a compressed fluid driven downhole cam motor foruse in drilling/well operations in the ground.

During directional drilling in a formation in the ground, e.g. duringhorizontal drilling of a well, it is common to use drilling equipmentcomprising a drill string, a drill string link and a drill bit. Thedrill string may be constituted by coiled tubing, and the drill bit maybe driven hydraulically by the fluid circulating in the drill string.The direction of drilling is changed by rotating the drill string link,and the rotation is performed by a tool disposed between the lower endof the drill string and the drill string link. In most known tools, therotation is not infinitely variable, but must be carried out at fixedangular deflections of the order of 15–20 degrees. This means that thedirection of drilling can not be changed with the desired accuracy.Another disadvantage of most known tools of this type is that the effortof the drill bit must be reduced in order to allow rotation of the drillstring link. A consequence of this may be that the drill bit looses itshold on the ground formation, causing the drill string link to return tothe initial position instead of completing the rotation. These areconditions that complicate and also delay the work of changing thedirection of drilling.

In other well operations, there may be a need for both volume- andpressure-controlled compressed fluid motors. Motors of this type, whichrotate continuously, has a high torque and also require little space,are not known.

Moreover, most cam motors according to prior art take up a relativelylarge amount of space in the longitudinal direction of the drillingdevice, are slow, and are not designed to rotate continuously.

The invention aims to remedy the disadvantages of prior art.

The aim is achieved in accordance with the invention by thecharacteristics given in the description below and in the followingclaims.

Radial piston motors are well suited to providing a relatively hightorque at modest overall dimensions. Nevertheless, it is difficult toachieve sufficiently high torque with the structural dimensions that canbe used in underground drilling tools. A radial piston motor accordingto the invention is provided with two or more co-ordinated sets ofradial pistons. One set of pistons is here taken to mean one set ofpistons as they are arranged in a radial piston motor or radial pistonengine of a type that is known per se. The pistons from the individualsets of pistons may be arranged so as to form axial banks, or arrangedin another geometrical pattern.

In a preferred embodiment, the pistons associated with each of theco-ordinated sets of pistons may be arranged along imaginary axial lineswith mutually equal separation about the central axis of the radialpiston motor. However, in order to be able to use a sufficient number ofpistons having sufficient dimensions, every other set of radial pistonsis rotated about said central axis, so that the pistons, when seen alongthe central axis, are positioned between the pistons of the adjacent setof pistons. This rotationally staggered arrangement of the pistonsallows more pistons to be assigned to a given volume without thecylinder bore of each individual piston coinciding with the cylinderbore of the adjoining cylinder. A distributing valve distributescompressed fluid to the pistons in accordance with techniques that areknown per se. The piston cylinders that form a bank along each of saidimaginary axial lines are connected to a common compressed fluid duct,which allows them to communicate and causes them to be displacedsimultaneously under the influence of compressed fluid while the cammotor rotates. Each bank of pistons abuts a common bearing cylinder,which in turn abuts the undulated interior of the cam motor casing. Thedetailed functioning of the cam motor will be explained in the specificpart of the description, with reference to the appended drawings.

Due to its small overall dimensions and potentially high torque, ahydraulic cam motor according to the invention is particularly wellsuited for use in downhole drilling devices.

In its basic configuration, the hydraulic cam motor is avolume-controlled actuator, as its angle of rotation depends directly onthe volume of compressed fluid flowing through the cam motor. In thismode of operation, the cam motor is well suited for tasks where theangle of rotation must be controlled with great accuracy, and also forcontinuous rotation.

By providing the cam motor with a flow-regulating valve, e.g. in theform of a bore/nozzle through which part of the compressed fluid maypass without passing through the cam motor, a certain pressure controleffect may be achieved. This may be explained by the fact that when thecam motor is not rotating, e.g. because it is not able to overcome themoment of resistance to rotation in question, the pressure drop acrossthe nozzle will determine the magnitude of the differential pressure towhich the cam motor is subjected. The pressure drop across the nozzle isdetermined by the volumetric flow through the nozzle. Thus upstream ordownstream flow regulating means may be used to regulate the torque ofthe cam motor. A volume- or pressure-controlled valve may for instancebe controlled so as to close/open the flow regulating bore/nozzle/valvetemporarily.

Start-up and shutdown of the cam motor may also be performed by usinge.g. arrangements of brakes and locks according to prior art, where avolume-controlled stop valve or throttle valve unloads/loads thebrake/lock arrangement and/or closes/opens for compressed fluid to thecam motor.

In an embodiment for continuous rotation, e.g. of the drill string linkfor the purpose of improving the flow conditions around the drillstring, the cam motor is equipped with a through flow orifice designedto lead the volume flow through the cam motor without any significantpressure drop. Compressed fluid flowing through the cylinders of the cammotor is drained to the outside of the cam motor. Thus the torque of thecam motor is directly proportional to the pressure drop of thecompressed fluid downstream of the cam motor.

The cam motor may also be used as a hydraulic pump, in principle withoutmodifications. The cam motor may also be designed so as to leave thepistons arranged in the intermediate casing, working against a profiledrotor.

The following describes a non-limiting example of a preferred embodimentillustrated in the accompanying drawings, in which:

FIG. 1 is a longitudinal sectional view of the cam motor;

FIG. 2 shows a cutout from FIG. 1 on a larger scale;

FIG. 3 is a sectional view of an alternative embodiment;

FIG. 4 is a sectional view of a further embodiment;

FIG. 5 is a sectional view of a further embodiment;

FIG. 6 is a sectional view of the cam motor of FIG. 2; and

FIG. 7 is a perspective, partly exploded view in which several of themain components of the cam motor are illustrated.

In the drawings, reference number 1 denotes a hydraulic cam motorcomprising an inlet coupling 2, an intermediate casing 4, a bearinghousing 6 and an outlet coupling 8. One end of the inlet coupling 2 isprovided with a threaded portion 10 that matches a connecting portion ofan upstream drill string (not shown) in a complementary manner, and atthe other end the inlet coupling 2 is rigidly connected to theintermediate casing 4 via thread 12. The intermediate casing 4 isrigidly connected to the bearing housing 6 via thread 13, while theinterior of the intermediate casing 4 is provided with a profiledsurface 14. The inlet coupling 2, the intermediate casing 4 and thebearing housing 6 form the external, rotationally static enclosure ofthe cam motor 1.

The projecting end portion of the outlet coupling 8 is provided with athreaded portion 16 that matches a connecting portion of a downstreamdrill string (not shown) in a complementary manner. The inside endportion of the outlet coupling 8 is connected to a rotor 18 via thread20, and is rotatably mounted in the bearing housing 6 via thrustbearings and radial bearings 22 a, 22 b, 22 c and 22 d. An internal nut23 prevents the bearings 22 a to 22 d from being displaced in thehousing 6. The outlet coupling 8 forms the output shaft of the cam motor1.

The inlet coupling 2 is provided with a through opening 24. Adistributing valve 26 is placed in the inlet coupling 2, where a gasket28 stops fluid flow between the inlet coupling 2 and the distributingvalve 26. The flange-like end portion 30 of the distributing valve 26 isdisposed in the intermediate casing 4 and fits in the profiled surface14 in the intermediate casing 4 in a complementary manner, and isthereby rigidly connected to the intermediate casing 4 rotational-wise.The distributing valve 26 is provided with a certain number of inletbores 32 and a corresponding number of outlet bores 34. The inlet bores32 connect the central chamber of the distributing valve 26 with thevalve facing 38. The outlet bores 34 connect the valve facing 38 withthe outlet port 40.

The rotor 18 is provided with a number of radial cylinder bores 42. Inthe preferred embodiment shown, the cylinders 42 are arranged in 12axial banks. The number of cylinders 42 in each bank is adjustedaccording to the desired torque of the cam motor 1. The cylinders 42 ofeach bank communicate with each other through a bore 44 that ends up inan end face 46 of the rotor 18. A radial piston 48 is arranged in eachcylinder 42. All pistons 48 located in a common bank of cylinders areconnected to a roller 50. The roller 50 is rotatably supported in thepistons 48, and abuts the profiled surface in the intermediate casing 4.The rotor 18 is provided with a bore 52 that forms an extension of thecentral through bore 53 of the outlet coupling 8, communicating with theoutlet port 40 via ports 54. A gasket 56 seals against fluid leaks fromthe central chamber 36 to the outlet port 40. The contact pressurebetween the valve facing 38 of the distributing valve 26 and the endface 46 of the rotor 18 is hydraulically balanced, in that the fluidpressure acts on that part of the net upstream cross-sectional area ofthe distributing valve 26 which is situated between the gaskets 28 and56.

The section in FIG. 6 shows six sets of radial pistons 48 withassociated cylinders 42, which sets form a set 68 of pistons such as isknown per se from conventional radial piston motors. The co-ordinatedset of pistons along the longitudinal axis of the rotor 18 can beshifted rotationally, so that the pistons in this set are situatedbetween the pistons in the adjacent sets of pistons, seen along thelongitudinal axis of the rotor 18. By arranging the sets of pistons insuch a rotationally staggered manner, more cylinders 42 may be placed ina rotor 18 without the cylinders getting too close to each other.

When the cylinder 42, see cylinder “A” in FIG. 6, is supplied withcompressed fluid through the bore 44, the piston 48 is displaced outtowards the roller 50 abutting one bevel 58 of the cam-shaped profiledsurface 14 in the intermediate casing 4. The rotor 18 is thereby causedto rotate in the direction of the arrow. Correspondingly, fluid mustflow out of the cylinder 42′ when the roller 50′ is displaced along theopposite bevel 60 of the cam-shaped profile, see cylinder “B” in FIG. 6.

On operation of the cam motor 1, compressed fluid flows through the bore24 of the inlet coupling 2 and into the central chamber 36 of thedistributing valve 26, and further into the inlet bores 32 of thedistributing valve 26. One or more of the inlet bores 32 correspondcompletely or partially with the bores 44 of the rotor 18, through whichthe cylinder 42 located by a bevel 58 on the intermediate casing 4 issupplied with compressed fluid. One or more of the outlet bores 34correspond completely or partially with bores 44′, through whichcylinders 42′ located by a bevel 60 drain compressed fluid. Thuscompressed fluid flows into cylinders 42, where the associated piston 48with roller 50 is displaced out towards the bevel 58. By so doing, therotor 18 is caused to rotate. When the piston 48 and the roller 50reaches the fully extended position, the inlet bore 32 no longercorresponds with the bore 44 in question, and the supply of compressedfluid stops. When the rotor is rotated further, the bore 44 correspondswith one of the outlet bores 34. Fluid flows out of the cylinder 42through the bore 44, the outlet bore 34, the outlet port 40, theopenings 54 and further through the bores 52 and 53. By several banks ofcylinders being in different positions relative to the cam-shapedprofile 14 in the intermediate casing 4, the cam motor 1 rotatescontinuously upon supply of compressed fluid, see FIG. 6.

In an alternative embodiment, see FIG. 3, the rotor 18 is provided witha through bore 62 that forms a throttle between the central chamber 36of the distributing valve 26 and the bore 52 of the rotor 18. The flowrate in the bore 62 depends on the pressure drop through the bore 62,and this design is used to achieve a certain amount of pressure controlof the cam motor 1, such as described in the general part of thedescription.

In a further embodiment, see FIG. 4, the bore 52 of the rotor 18 isthrough-going, and the outlet port 40 has been removed. In thisembodiment, the outlet bores 34 communicate with the outside of theenclosure of the cam motor 1 through bores 64 and 66. In thisembodiment, the torque of the cam motor 1 is directly dependent on adownstream back pressure.

In a further embodiment, see FIG. 5, the cam motor 1 is provided with avolume-controlled throttle/stop valve 70. The compressed fluid flowsthrough the valve-70-bore 72, at a certain flowrate overcoming the forcefrom a spring 74, whereby the valve 70 is displaced to stop compressedfluid flowing into the inlet bores 32. The cam motor 1 may if sorequired be equipped with a free wheel 76 of a type that is known perse, which prevents the rotor 18 from rotating in the opposite rotatingdirection relative to the working direction when the supply ofcompressed fluid is shut off. By reducing the flow of compressed fluid,the force from the spring 74 overcomes the force of the compressedfluid, so that the valve 70 is displaced to its inactive position,whereupon the cam motor 1 starts up again. When compared to known cammotors for downhole applications, the cam motor 1 distinguishes itselfby achieving a relatively high torque while having modest overalldimensions, and by being designed to be rotated continuously whilstbeing simple to control in respect of angle of rotation, moment andspeed.

1. A compressed fluid driven downhole cam motor, comprising: anintermediate casing in which a rotor and a distributing valve arearranged along an essentially common central axis, and two or morepistons arranged radially about the central axis of the rotor, wherebythose pistons that are located in the same radial plane constitute a setof pistons, characterized in that two or more sets of pistons arearranged side by side along a longitudinal axis of the rotor; such thatat least one piston from each of two or more sets of pistons share acommon flow path for fluid communication with the distributing valve. 2.A device in accordance with claim 1, wherein two adjacent sets ofpistons are placed in a rotationally staggered manner about the centralaxis of the rotor, so that the pistons of one set of pistons are locatedbetween the pistons of the adjacent set(s) of pistons.
 3. A device inaccordance with claim 1, wherein a roller is rotatably supported in twoor more of the pistons.
 4. A device in accordance with claim 3, whereina contact pressure between a valve facing of the distributing valve andan end face of the rotor is hydraulically balanced.
 5. A device inaccordance with claim 1, wherein the cam motor is provided with athrottle in the rotor.
 6. A device in accordance with claim 1, whereinthe cam motor is provided with a through bore in the rotor.
 7. A devicein accordance with claim 1, wherein the cam motor is provided with apressure volume-controlled stop valve designed to shut off a supply ofcompressed oil to an inlet born.
 8. The motor of claim 1, wherein thecommon flow path is parallel with the central axis of the motor.
 9. Thedevice of claim 1, wherein the common flow path is substantiallyparallel to the common central axis.
 10. A drilling system for forming awellbore, comprising: a drill string; a downhole motor having: a rotorand a distributing valve arranged along an essentially common centerline; and two or more sets of pistons arranged side by side along anaxis of the rotor, wherein each of the two or more sets of pistonscomprises two or more pistons arranged radially about the axis of therotor and located in the same radial plane; and wherein at least onepiston from each of two or more sets of pistons share a common flow pathfor fluid communication with the distributing valve; and a drillingmember rotatable by the downhole motor.
 11. The drilling system of claim10, wherein two adjacent sets of pistons are placed in a rotationallystaggered manner.
 12. The drilling system of claim 10, wherein a rolleris rotatably supported in two or more of the pistons.
 13. The drillingsystem of claim 10, further comprising a drill string link for changinga direction of drilling.
 14. The drilling system of claim 10, whereinthe at least one pistons from each of two or more sets of pistonssharing the common flow path are displaced simultaneously.
 15. Thedrilling system of claim 10, wherein the common flow path is alternatelyplaced in fluid communication with an inlet bore and an outlet bore. 16.A method of forming a wellbore, comprising: providing a downhole motorhaving: a rotor; a distributing valve coupled to the rotor; and two ormore sets of pistons arranged side by side along an axis of the rotor,wherein each of the two or more sets of pistons comprises two or morepistons arranged radially about the axis of the rotor and located in thesame radial plane; and wherein at least one piston from each of two ormore sets of pistons share a common flow path for fluid communicationwith the distributing valve; lowering the downhole motor into thewellbore; and actuating the downhole motor to rotate a drilling membercoupled to the downhole motor, thereby forming a wellbore.
 17. Themethod of claim 16, further comprising simultaneously displacing the atleast one pistons sharing the common flow path.
 18. The method of claim16, further comprising altering a trajectory of the wellbore.
 19. Themethod of claim 16, further comprising hydraulically balancing a contactpressure between a valve facing of the distributing valve and an endface of the rotor.
 20. The method of claim 16, further comprisingpositioning the pistons of adjacent sets of pistons in a staggeredmanner.
 21. A compressed fluid driven downhole cam motor, comprising: anintermediate casing in which a rotor and a distributing valve arearranged along an essentially common center line; two or more sets ofpistons are arranged side by side along a longitudinal axis of therotor, wherein each set of pistons includes two or more pistons arrangedradially about the longitudinal axis of the rotor and in the same radialplane; and a pressure volume-controlled stop valve designed to shut offa supply of compressed oil to an inlet bore of the distributing valve.